Yes, the double-slit experiment does exhibit a change in behavior when it is observed, specifically when there is a measurement or observation made to determine which path the particle takes.
In the double-slit experiment, a beam of particles, such as electrons or photons, is directed toward a barrier with two slits. When the particles pass through the slits, they create an interference pattern on a screen placed behind the barrier. This pattern suggests that the particles exhibit wave-like behavior, as if they have passed through both slits and interfered with themselves.
However, if one tries to determine which path the particle takes, for example, by placing detectors at the slits or by observing the particles as they pass through, the interference pattern disappears. Instead, the particles behave like classical particles, and each particle appears to go through one slit or the other, producing a pattern consistent with the sum of the two individual slit patterns.
This phenomenon is known as the "collapse of the wave function" or "quantum measurement." When a measurement is made to determine which path the particle takes, it forces the particle to "choose" one of the two possible paths and loses the wave-like behavior that produces the interference pattern. The act of observation or measurement disturbs the quantum system and causes it to behave classically.
The change in behavior when observed is a fundamental aspect of quantum mechanics and is often referred to as the measurement problem or the observer effect. It highlights the delicate and intricate nature of quantum systems, where the act of measurement fundamentally alters the state of the system.
It is worth noting that the exact interpretation and understanding of the measurement problem are still subjects of debate and ongoing research in quantum mechanics. Various interpretations, such as the Copenhagen interpretation or the many-worlds interpretation, offer different perspectives on how to understand and explain the change in behavior during observation.